package network;

import java.io.IOException;
import java.net.*;
import java.util.Scanner;

public class UdpEchoClient {
    private DatagramSocket socket = null;
    private String serverIP;
    private int serverPort;
    public UdpEchoClient(String serverIP,int serverPort) throws SocketException {
        //对于客户端来说，不需要显示关联端口
        //这并不代表客户端没有端口，而是让系统自动分配空闲的端口
        socket = new DatagramSocket();
        this.serverIP = serverIP;
        this.serverPort = serverPort;
    }
    //启动客户端
    public void start() throws IOException {
        //通过这个客户端可以多次和服务器仅从交互
        Scanner scanner = new Scanner(System.in);
        while(true){
            //1.先从控制台，读取一个字符串
            System.out.println("-> ");//打印一个提示符，提示用户要输入内容
            String request = scanner.next();
            //2.把字符串构造成UDP数据报，并进行发送
           DatagramPacket requestPacket = new DatagramPacket(request.getBytes(),
                   request.getBytes().length,
                    InetAddress.getByName(serverIP),serverPort);
           socket.send(requestPacket);
            //3.客户端尝试读取服务器返回的响应
            DatagramPacket responsePacket = new DatagramPacket(new byte[4096],4096);
            socket.receive(responsePacket);
            //4.把响应数据转换成String显示出来
            String response = new String(responsePacket.getData(),0,
                    responsePacket.getLength());
            System.out.printf("req: %s,resp: %s\n",request,response);
        }
    }

    public static void main(String[] args) throws IOException {
        UdpEchoClient udpEchoClient = new UdpEchoClient("127.0.0.1",9090);
        udpEchoClient.start();
    }
}
